Cucumber benefits: it is 95.2% water — and the trials used extracts, not cucumber

Key benefits

1. 01Nutrition data

   It is 95.2% water — and that fact is what this vegetable is for

   Per 100 g of raw cucumber with the peel:

   • Water 95.2%
   • 15 kcal
   • Potassium 147 mg
   • Carbohydrate 3.63 g, sugar 1.67 g, fibre 0.5 g
   • Protein 0.65 g, fat 0.11 g
   • Phosphorus 24 mg, calcium 16 mg, magnesium 13 mg
   • Vitamin C 2.8 mg, folate 7 µg, beta-carotene 45 µg
   • Sodium 2 mg

   It is easy to look at this and conclude there is nothing here. That is half right.

   The vitamin and mineral content is low. Vitamin C at 2.8 mg is 3% of the daily value, clearly low against other vegetables.

   	Energy (100 g)	Vitamin C	Fibre
   Cucumber	15 kcal	2.8 mg	0.5 g
   Lettuce	15 kcal	9.2 mg	1.3 g
   Tomato	18 kcal	13.7 mg	1.2 g
   Broccoli	34 kcal	89.2 mg	2.6 g
   Watercress	11 kcal	43 mg	0.5 g

   But what this vegetable actually does lies elsewhere.

   First, it fills volume without energy. Fifteen kcal per 100 g; about 30 for a medium cucumber. Fill a side dish with cucumber and the bowl does not look empty while almost nothing goes into the day's total. That is arithmetic, not a trial.

   Second, sodium is 2 mg — effectively none. And potassium is 147 mg. A Korean table tends to be high in sodium, and a vegetable with none of it and some potassium sits on the other side of that.

   Third, the water. Being 95.2% water means eating cucumber is drinking water. But writing "hydration" up as a special benefit of cucumber is an overstatement — drinking water is faster and more certain.

   Do not peel it. Vitamin K, fibre and beta-carotene concentrate towards the skin. The USDA lists peeled cucumber separately, and the figures are lower.

   About bitterness. Cucumber bitterness comes from cucurbitacins, concentrated towards the stem end and varying by variety and growing conditions.

   Do not eat a very bitter cucumber. Cases of severe gastrointestinal illness have been reported from cucurbit vegetables high in cucurbitacins. If it tastes strongly bitter, spit it out and discard it. This is rare in normal commercial cucumbers.

   Choosing and keeping.

   • Pick firm and heavy ones. Soft or wrinkled at one end means it has been sitting
   • Cold refrigeration does not suit cucumbers. Held below 10°C for long they soften and pit. Wrap in paper and stand them upright in the crisper drawer
   • They are sensitive to ethylene. Do not store them with apples, bananas or tomatoes
2. 02Not established

   Three clinical trials — and all of them used extracts, not cucumber

   There are three randomised human trials on cucumber. All three used extracts.

   2017, Journal of Food Science — seed extract and lipids.

   • Adults with hyperlipidemia
   • Randomised, double-blind, placebo-controlled
   • Cucumber seed extract (Cucumis sativus seed extract)
   • Serum lipids measured

   The design is sound. But what it used was a preparation extracted from the seeds.

   Cucumber seeds are normally eaten as they are — nobody collects and extracts them. And extraction selects and concentrates particular compounds. What arrives when you eat a cucumber differs in both amount and composition.

   2018, Clinical Interventions in Aging — extract and knee osteoarthritis.

   • Patients with moderate knee osteoarthritis
   • Multicentre randomised comparative trial
   • Cucumber extract against glucosamine-chondroitin

   Note that the comparator is not a placebo but another supplement. So the result is not "cucumber extract beats taking nothing" but "cucumber extract compared thus against glucosamine-chondroitin" — and the effect of glucosamine-chondroitin itself is debated.

   2023, Current Rheumatology Reviews carries a placebo-controlled study of a standardised cucumber extract on osteoarthritis measures. An extract again.

   This is exactly the structure of this site's celery entry. Just as celery's blood pressure trial used 1.34 g of seed extract in capsules, cucumber's trials are not cucumber.

   So the grade is "not established".

   Stated precisely:

   • A trial found cucumber seed extract acting on lipids — that is not eating a cucumber
   • A trial found cucumber extract acting on knee osteoarthritis measures — that is not eating a cucumber either
   • A trial that fed cucumber and measured blood pressure, lipids, weight, joints or skin against a control is something this site could not find

   If you are considering a cucumber extract supplement, that is a different product from the vegetable, and it is hard to verify whether it reproduces the dose and formulation of those trials.

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3. 03Not established

   Weight loss, detox, puffiness, skin — the common claims

   The "cucumber diet".

   It is true that it is low in energy. Fifteen kcal per 100 g, and filling space with cucumber instead of other food lowers the day's total. That is arithmetic from the composition, not a benefit.

   But a cucumber-only diet is not advisable. Protein is 0.65 g, fat 0.11 g, and vitamins and minerals are low. Replacing meals with a single food is not advisable with any food.

   "Detox" and "detox water".

   Putting cucumber and lemon in water is a familiar idea. If it tastes better and you therefore drink more water, that is useful in itself.

   But "detox" is not a medically defined term. A claim about removing something from the body only means anything if it says what, how much, and measured how. And the amount of anything that steeps out of cucumber into water is very small.

   "It reduces puffiness."

   The explanation given is potassium and sodium excretion. Cucumber's potassium is 147 mg per 100 g. Banana is 358, spinach 558. If potassium is the goal, cucumber is not a good choice.

   And this site found no trial that fed cucumber, measured swelling and compared against a control.

   "Slices on the eyes reduce puffiness."

   Anything cold on the eyes constricts blood vessels and makes puffiness look temporarily less. That is what cold does, not cucumber. A chilled spoon or a damp towel does the same.

   On applying it to skin. Cucumber itself is mild and rarely a problem. But do not use it on broken or inflamed skin. And expecting coolness is more accurate than expecting an effect.

   To summarise:

   • Confirmed by composition: 95.2% water, 15 kcal, potassium 147 mg, sodium 2 mg
   • Not confirmed: blood pressure, lipids, weight, swelling, skin — no trial fed cucumber and measured them
   • From extracts: seed extract and lipids (2017), extract and knee osteoarthritis (2018 and 2023)
   • Useful facts: it fills volume without energy, and has almost no sodium

   This is not a reason to stop eating it. It tastes good, it is low in energy, and it has no sodium. It is a reason not to inflate that into "benefits".

How to eat it well

What to watch out for